Removable stent for body lumens

ABSTRACT

A removable stent for implantation into a lumen in a human body. The stent is made from a soft, flexible fiber having an outer surface. An outer bioabsorbable/degradable coating is applied to the outer surface of the flament causing it to become rigid. The coating softens in vivo through absorption and/or degradation such that the stent is readily passed or removed from the lumen as a softened filament after a pre-determined period of time through normal flow of body fluids passing through the lumen or by manual removal.

FIELD OF THE INVENTION

[0001] The field of art to which this invention relates is medicaldevices, in particular, removable stent devices having bioabsorbable orbiodegradable polymer coatings.

BACKGROUND OF THE INVENTION

[0002] The use of stent medical devices, or other types of endoluminalmechanical support devices, to keep a duct, vessel or other body lumenopen in the human body has developed into a primary therapy for lumenstenosis or obstruction. The use of stents in various surgicalprocedures has quickly become accepted as experience with stent devicesaccumulates, and the number of surgical procedures employing themincreases as their advantages become more widely recognized. Forexample, it is known to use stents in body lumens in order to maintainopen passageways such as the prostatic urethra, the esophagus, thebiliary tract, intestines, and various coronary arteries and veins, aswell as more remote cardiovascular vessels such as the femoral artery,etc. There are two types of stents that are presently utilized:permanent stents and temporary stents. A permanent stent is designed tobe maintained in a body lumen for an indeterminate amount of time.Temporary stents are designed to be maintained in a body lumen for alimited period of time in order to maintain the patency of the bodylumen, for example, after trauma to a lumen caused by a surgicalprocedure or an injury. Permanent stents are typically designed toprovide long term support for damaged or traumatized wall tissues of thelumen. There are numerous conventional applications for permanent stentsincluding cardiovascular, urological, gastrointestinal, andgynecological applications.

[0003] It is known that permanent stents, over time, become encapsulatedand covered with endothelium tissues, for example, in cardiovascularapplications. Similarly, permanent stents are known to become covered byepithelium, for example, in urethral applications. Temporary stents, onthe other hand are designed to maintain the passageway of a lumen openfor a specific, limited period of time, and preferably do not becomeincorporated into the walls of the lumen by tissue ingrowth orencapsulation. Temporary stents may advantageously be eliminated frombody lumens after a predetermined, clinically appropriate period oftime, for example, after the traumatized tissues of the lumen havehealed and a stent is no longer needed to maintain the patency of thelumen. For example, temporary stents can be used as substitutes forin-dwelling catheters for applications in the treatment of prostaticobstruction or other urethral stricture diseases. Another indication fortemporary stents in a body lumen is after energy ablation, such as laseror thermal ablation, or irradiation of prostatic tissue, in order tocontrol post-operative acute urinary retention or other body fluidretention.

[0004] It is known in the art to make both permanent and temporarystents from various conventional, biocompatible metals. However, thereare several disadvantages that may be associated with the use of metalstents. For example, it is known that the metal stents may becomeencrusted, encapsulated, epithelialized or ingrown with body tissue. Thestents are known to migrate on occasion from their initial insertionlocation. Such stents are known to cause irritation to the surroundingtissues in a lumen. Also, since metals are typically much harder andstiffer than the surrounding tissues in a lumen, this may result in ananatomical or physiological mismatch, thereby damaging tissue oreliciting unwanted biologic responses. Although permanent metal stentsare designed to be implanted for an indefinite period of time, it issometimes necessary to remove permanent metal stents. For example, ifthere is a biological response requiring surgical intervention, oftenthe stent must be removed through a secondary procedure. If the metalstent is a temporary stent, it will also have to be removed after aclinically appropriate period of time. Regardless of whether the metalstent is categorized as permanent or temporary, if the stent has beenencapsulated, epithelialized, etc., the surgical removal of the stentwill resultingly cause undesirable pain and discomfort to the patientand possibly additional trauma to the lumen tissue. In addition to thepain and discomfort, the patient must be subjected to an additional timeconsuming and complicated surgical procedure with the attendant risks ofsurgery, in order to remove the metal stent.

[0005] Similar complications and problems, as in the case of metalstents, may well result when using permanent stents made fromnon-absorbable biocompatible polymer or polymer-composites althoughthese materials may offer certain benefits such as reduction instiffness.

[0006] It is known to use bioabsorbable and biodegradable materials formanufacturing temporary stents. The conventional bioabsorbable orbioresorbable materials from which such stents are made are selected toabsorb or degrade over time, thereby eliminating the need for subsequentsurgical procedures to remove the stent from the body lumen. In additionto the advantages attendant with not having to surgically remove suchstents, it is known that bioabsorbable and biodegradable materials tendto have excellent biocompatibility characteristics, especially incomparison to most conventionally used biocompatible metals in certainsensitive patients. Another advantage of stents made from bioabsorbableand biodegradable materials is that the mechanical properties can bedesigned to substantially eliminate or reduce the stiffness and hardnessthat is often associated with metal stents, which can contribute to thepropensity of a stent to damage a vessel or lumen.

[0007] However, there are disadvantages and limitations known to beassociated with the use of bioabsorbable or biodegradable stents. Thelimitations arise from the characteristics of the materials from whichsuch stents are made. One of the problems associated with the currentstents is that the materials break down too quickly. This improperbreakdown or degradation of a stent into large, rigid fragments in theinterior of a lumen, such as the urethra, may cause obstruction tonormal flow, such as voiding, thereby interfering with the primarypurpose of the stent in providing lumen patency. Alternatively, theytake a long time to breakdown and stay in the target lumen for aconsiderable period of time after their therapeutic use has beenaccomplished. There is thus a long-term risk associated with thesematerials to form stones when uretheral stents made from longerdegrading biodegradable polymers.

[0008] Accordingly, there is a need in this art for novel, temporarystents, wherein the stents remain functional in a body lumen for theduration of a prescribed, clinically appropriate period of time toaccomplish the appropriate therapeutical purpose, and, then soften andare removable as an elongated string-like member without producingfragments, which may cause irritation, obstruction, pain or discomfortto the patient, and without the need for a surgical procedure.

[0009] In a preferred embodiment of the present invention, the temporarystent readily passes out of the body, or is removed as, a limp, flexiblestring-like member, and irritation, obstruction, pain or discomfort tothe patient is either eliminated, or if present, is minimal.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a stent forinsertion into a body lumen which is manufactured from a flexiblefilament member, such as a suture, and then coated with a biodegradableor bioabsorbale polymer such that the member is formed into a relativelyrigid stent, and when in the body, softens back into a flexible filamentmember which is easily passed or removed from the body lumen after aspecific therapeutic period of time.

[0011] Therefore, an implantable stent is disclosed for use in bodylumens, wherein such lumens exist as part of the natural anatomy or aremade surgically. The stent is an elongate, hollow member having ahelical or coiled structure, and in a preferred embodiment has a helicalstructure having a plurality of coils. The structure has a longitudinalaxis and a longitudinal passage. The coils have a pitch. The structureis made from a flexible, limp filament or fiber, such as a surgicalsuture, having an exterior polymeric coating. The polymeric coating is abioabsorbable or biodegradable polymer, or blend thereof At bodytemperature, the coating is solid, and of sufficient thickness toeffectively cause the flexible, limp member to be maintained in asubstantially rigid, fixed state as a structure. The rate of degradationor absorption of the coating in vivo is sufficient to effectively softenor be removed from the outer surface of the filament within the desiredtherapeutic period. This effectively provides that as the coatingdegrades, softens or is absorbed in vivo, it loses its mechanicalintegrity. This allows the filament to revert to its natural, flexiblelimp state, causing the stent structure to effectively collapse, and thefilament may be removed or eliminated from the lumen.

[0012] Upon in vivo exposure to body fluids, the progressively degradingand/or absorbing coating causes the stent to soften and collapse into aflexible filament that can readily pass out of the body lumen, either bymanipulation or through natural expulsion with body fluids, therebyminimizing the possibility of causing obstruction, pain or discomfort.

[0013] Yet another aspect of the present invention is theabove-described stent made from a fiber which is radio-opaque.

[0014] Yet another aspect of the present invention is a method of usingthe stents of the present invention in a surgical procedure to maintainthe patency of a body lumen. A stent of the present invention isprovided. The stent is an elongate, hollow member and in a preferredembodiment has a helical structure having a plurality of coils. Themember has a longitudinal axis. The coils have a pitch. The structure ismade from a flexible, limp filament or a fiber, having an outer surfaceand an exterior polymeric coating. The stent is inserted into a bodylumen. The exposure to in vivo body fluids causes the exterior coatingto absorb and/or degrade and soften, thereby causing the stent structureto collapse and return to a limp, flexible filament that can then beeither eliminated by the passage of body fluids or manually removed.

[0015] These and other aspects of the present invention will become moreapparent from the following description and examples, and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a perspective view of a preferred embodiment of a stentdevice of the present invention mounted to the distal end of anapplicator instrument.

[0017]FIG. 2 is a perspective view of the stent and applicator of FIG.1, prior to loading the stent onto the applicator instrument.

[0018]FIG. 3 is a side view of a stent device of the present invention,having a helical configuration.

[0019]FIG. 4 is a cross-sectional view of the fiber used to make thestent of FIG. 3 taken along View Line 4-4 illustrating a circularcross-section.

[0020]FIG. 5 is a side view of the stent and applicator device of FIG.1, where the device is shown in the ready position, prior toapplication.

[0021]FIG. 6 is a side view of the stent and applicator device of FIG.5, illustrating the position of the stent relative to the applicatorwhen the stent is partially deployed by engaging the applicator trigger.

[0022]FIG. 7 illustrates the relative positions of the stent to theapplicator of FIG. 6 when the stent is fully deployed by fully engagingthe applicator trigger.

[0023]FIG. 8 illustrates the stent of the present invention fullydeployed in the urethra and prostate of a patient, providing for apatent lumen.

[0024]FIG. 9 illustrates a stent of the present invention emplaced inthe urethra of a patient after the coating has degraded, been absorbedor otherwise broken down or softened; showing the stent being removedfrom the body as an elongated, soft, flexible filament.

[0025]FIG. 10 is a schematic of a mandrel used to manufacture stents inExample 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Referring to FIGS. 1-9, a preferred embodiment of a stent of thepresent invention is illustrated. As seen in FIG. 3, the stent 10 isseen to be a helical structure having a series of connected coils 20.The coils are made from filament 100. The term filament as used hereinis defined to include not only filaments but fibers as well, and is usedinterchangeably with the term fiber. It is preferred that filament 100be a continuous filament, however, it is possible to make stent 10 fromtwo or more sections of filament which are subsequently connected orhinged together. As seen in FIG. 4, the filament 100 is seen to haveinner flexible member 110 and outer coating 130. The inner flexiblemember 110 is seen to have outer surface 115. Covering the outer surface115 of flexible member 110 is the outer coating 130. Outer coating 130is seen to have inner surface 135 and exterior surface 140. Preferably,inner surface 135 is in contact with, and affixed to, the outer surface115. The stent is seen to have a longitudinal axis 70, and internalpassageway 11. The stent 10 is seen to have a first distal section 30 ofcoils 20 connected to a second section 50 of coils 20, wherein thesections 30 and 50 are connected by hinged connecting fiber 60. Thedistal section 30 of coils adjacent to hinged connecting fiber 60 formsan anchoring section which is inserted distal to the external sphincter.The proximal section 50 of the stent 10 is maintained within theprostatic urethra. Proximal section 50 is seen to have coils 20 havingdiameter 24, and also has passageway 51. The distal section 30 of stent10 has coils 20 having a diameter 22. Distal section 30 also has apassageway 31. Passage ways 31 and 51 are in communication to formpassageway 11 of stent 10. As seen in FIG. 4, one preferred embodimentof the stent 10 of the present invention has a filament 100 having acircular cross-sectional configuration. The filament 100 may havevarious configurations depending upon the application including round,square, polygonal, curved, oval, and combinations thereof andequivalents thereof. Those skilled in the art will appreciate thatcertain cross-sectional configurations will provide different advantagesin the stent. For example, the advantages of fiber of the presentinvention having a round cross-section include ease of the stentmanufacturing process due to a possible on-line, one-step transitionfrom the fiber to the stent in future manufacturing processes,flexibility during the stent deployment by being able to tailor thelength of the stent during a surgical procedure to fit a particularpatient's anatomy, and the use of commercially available filaments suchas sutures.

[0027] The stent 10 is preferably manufactured from a flexible,polymeric filament 100 having a desired cross-sectional configuration.The length and overall diameter of the stent 10 will depend upon anumber of factors including the anatomy of the patient, the size of theanatomy and the type of surgical procedure which has effected theurethral lumen. For example, the overall length of a stent 10 useful inthe practice of the present invention will be sufficient to effectivelymaintain the lumen passage open. Typically the length for urethralapplications in and adult male, the length will be about 10 mm to about200 mm, more typically about 20 mm to about 100 mm, and preferably about40 mm to about 80 mm. The diameter of a stent 10 of the presentinvention will be sufficient to effectively maintain patency of thelumen. For prostatic urethral applications, where the stent has twosections having different diameters, typically the diameter in theprostatic urethra will typically be about 2 mm to about 25 mm, moretypically about 4 mm to about 15 mm, and preferably about 6 mm to about10 mm. The diameter of the section used to anchor distal to the externalsphincter will be about 2 mm to about 25 mm, more typically about 4 mmto about 15 mm, and preferably about 6 mm to about 10 mm. The majorcross-sectional dimension of a fiber used to manufacture a stent of thepresent invention will be sufficient to provide effective support andflexibility. Typically, when utilizing a circular cross-section, thediameter for urethral applications will be about 0.1 mm to about 4 mm,more typically about 0.5 mm to about 3 mm, and preferably about 1 mm toabout 2 mm. The pitch, length, diameter and fiber diameter of the stentsof the present invention will be sufficient to effectively providesufficient support in response to radial stress of the urethral vesselwalls, while providing for ease of insertion and stability whileinserted in the urethral lumen, as well as desired flexibility and lumenpatency. The pitch of the stent is defined to be the number of coils perunit length. In this patent application specification, for this example,pitch is defined as the number of coils per centimeter of stent length.Typically, for urethral applications, the pitch will be about 2.5 toabout 100, more typically about 3 to about 20, and preferably about 5 toabout 10. Although it is preferred for urethral applications that therebe no space between adjacent coils, the stents of the present inventionmay have spaces between adjacent coils.

[0028] The flexible members 110 coated with coatings 130 to formfilaments 100 of the present invention will preferably be selected tohave sufficient flexibility and softness and limpness to effectivelyprovide for a stent that will collapse and be easily removed from a bodylumen. The materials useful for the flexible member include flexible,limp monofilament and braided string-like members. It is particularlypreferred to use conventional nonabsorbable sutures, such asmonofilament or braided polypropylene, silk, polyester, nylon and thelike and equivalents thereof The flexible members may also beconventional absorbable sutures, monofilament or braided, including 95/5lactide/glycolide, and polydioxanone, and the like. The flexible member110 may also be made from yarn type materials made from biocompatiblefibers that are “spun” together to form the yarn.

[0029] The outer coatings useful for the stents and filaments of thepresent invention will be conventional biodegradable or bioabsorbablepolymers, and blends thereof, including polymers made from monomersselected from the group consisting of lactide, glycolide,para-dioxanone, caprolactone, and trimethylene carbonate, blends thereofand copolymers thereof The effect of the degradation or absorption ofthe polymeric coating is to convert the filament back into a soft,flexible member after a predetermined time period, such that the stenteffectively collapses, and the flexible member can then be easilyremoved or passed from the lumen. In a flow environment, theprogressively degrading stent can readily pass through the body or beremoved from the lumen without causing obstruction. The types ofpolymeric coatings that can advantageously provide stiffness to form afilament 100 include polymers with glass transition temperatures aboveroom temperature and preferably above 55° C., and most preferably aboveabout 120° C. These materials may be amorphous, that is, not displaycrystallinity. Polymers that have glass transition temperatures that arelow, especially below room temperature, will generally require somecrystallinity to provide the dimensional stability and stiffness tofunction in the present application. These can be described assemicrystalline. Regarding water soluble polymers for the coating, thereare two general classes of water soluble polymers: ionic and non-ionic.In general of use are polyacrylamides, polyacrylic acid polymers,polyethers (especially the polyethylene glycols or polyethylene oxides),vinyl polymers such as some polyvinyl alcohols and some poly(N-vinylpyrrolidone)s. Certain polysaccharide gums may also be useful; certainhydroxy celluloses, such as hydroxy methyl cellulose or certain hydroxyisopropyl cellulose are also useful.

[0030] One can control the dissolution process by material selection.Altering molecular weight of the water soluble resin also provides ameans of control.

[0031] Utilization of polymer blending is particularly advantageous toachieve the necessary rates of dissolution. Polyamide (nylon) may beused as a component to advantage because it can provide mechanicalstrength, absorbs some water, etc.

[0032] A possible preferred blend component is polyethylene glycol (PEGor polyethylene oxide, PEO), especially those higher molecular weightresins that are semicrystalline. The melting point of PEG is about 60°C., which is high enough to meet requirements of a coating useful in thepresent invention. Optionally, the PEO may be blended with nylon. Inaddition, biodegradable polymers made from poly glycolide/lactidecopolymers, polycaprolactone, and the like may be used for the outercoating of the filament 100. In addition, polyoxaesters can be utilizedwhich are water soluble and degrade by hydrolysis. Other suitablepolymers are found in U.S. Pat. No. 5,980,551, which is incorporated byreference.

[0033] A stent must be designed to withstand radial stresses in order toperform its function of maintaining a passage through a lumen open. Themechanical capability of the stents of the present invention towithstand radial stresses when the stent is emplaced in the body lumenis provided primarily by the biodegradable/bioabsorbable material in theouter coating. The strength and stiffness and thickness of this materialin the outer coating is sufficient to be effectively withstand the loadsnecessary to keep the stent functional. As the coating degrades andbreaks down, it will have a sufficient thickness of properly selectedbiodegradable material to effectively be able to withstand the loadnecessary for the time period required to keep the lumen patent. Inessence then, the coating can be designed to fulfill the mechanicalrequirements of keeping the body lumen patent or open for the specifictherapeutic time period.

[0034] After the coating has degraded/absorbed and effectively beenremoved from the stent structure by body fluids, the remaining filamentreturns to its soft, pliable, fibrillar state as a flexible member. Theremaining soft filament is readily excreted or removed from the lumen.

[0035] The coated filaments of the present invention may be made byconventional processes including co-extrusion, melt coating, solutioncoating or powder coating followed by spreading the coating by melting,etc., and the like. For example, when using a coating process, the innerflexible member can be a mono-filament extruded material or can be madefrom a multi-filament braid. The outer coating can be added on top ofthe flexible member either by melt coating or solution coating bypassing the inner core through a bath, through coating rollers, brushes,spraying and/or a die.

[0036] In another embodiment of the present invention, the polymers andblends that are used to form the coating can be used as a drug deliverymatrix. To form this matrix, the coating material would be mixed with atherapeutic agent. The variety of different therapeutic agents that canbe used in conjunction with the polymers of the present invention isvast. In general, therapeutic agents which may be administered via thepharmaceutical compositions of the invention include, withoutlimitation: anti-infectives such as antibiotics and anti-viral agents;analgesics and analgesic combinations; anti-inflammatory agents;hormones such as steroids; bone regenerating growth factors; andnaturally derived or genetically engineered proteins, polysaccharides,glycoproteins, or lipoproteins.

[0037] Matrix formulations may be formulated by mixing one or moretherapeutic agents with the polymer. The therapeutic agent, may bepresent as a liquid, a finely divided solid, or any other appropriatephysical form. Typically, but optionally, the matrix will include one ormore additives, such as diluents, carriers, excipients, stabilizers orthe like.

[0038] The amount of therapeutic agent will depend on the particulardrug being employed and medical condition being treated. Typically, theamount of drug represents about 0.001 percent to about 70 percent, moretypically about 0.001 percent to about 50 percent, most typically about0.001 percent to about 20 percent by weight of the matrix. The quantityand type of polymer incorporated into the drug delivery matrix will varydepending on the release profile desired and the amount of drugemployed.

[0039] Upon contact with body fluids, the polymer coating undergoesgradual degradation (mainly through hydrolysis) or absorption withconcomitant release of the dispersed drug for a sustained or extendedperiod. This can result in prolonged delivery (over, say 1 to 5,000hours, preferably 2 to 800 hours) of effective amounts (say, 0.0001mg/kg/hour to 10 mg/kg/hour) of the drug. This dosage form can beadministered as is necessary depending on the subject being treated, theseverity of the affliction, the judgment of the prescribing physician,and the like. Following this or similar procedures, those skilled in theart will be able to prepare a variety of formulations.

[0040] The stents 10 of the present invention when made from the coatedfilament 100 may be manufactured in the following manner using a windingprocess. A filament 100 is wound about a mandrel by heating the filament100 and then coiling it around the mandrel. The assembly of the mandreland the coil are annealed under constraint and then the mandrel isremoved. The pitch and diameter of the coils are selected to provide thedesired size and shape of stent. If desired, the filament 100 may bewound about the mandrel without heat, for example immediately uponentering a coating bath or melt bath, or the uncoated flexible member110 can be wound about a mandrel, and then the coating can be applied ina conventional manner, and cured as necessary.

[0041] The stents of the present invention may be utilized in thefollowing manner in urethral stent placement procedures as illustratedin FIGS. 1, 2, 5, 6, 7 and 8. Initially a stent 10 is placed upon thedistal end of an applicator instrument 200. Instrument 200 is seen tohave handle 250 having grip 255. At the top 257 of the handle 250 ismounted the shaft retention member 290. Retention member 290 is seen tohave longitudinal passageway 292, front 295 and back 296. The mountingtube 240 is seen to have distal end 242 and proximal end 244. Mountingtube 240 is seen to have passage 248. The proximal end 244 of tube 240is seen to be mounted in passage way 292 such that the inner passageway248 is in communication with passageway 292. Slidably mounted inpassageway 248 is the applicator tube 220. Tube 220 has distal end 222,proximal end 224, and passageway 226. Mounted to the proximal end 224 oftube 220 is the mounting block 300, which is affixed to end 224 by pin309. Mounted to the bottom of block 300 is rack gear member 330 havinggear teeth 335. Contained in handle 250 is the cavity 350 for receivingpinion gear member 270, having teeth 275. Pinion gear member 270 ispivotally mounted in cavity 350 by pivot pins 265. Teeth 275 mesh withand are engaged by teeth 335. Extending out from pinion gear member 270on the opposite side of pins 265 is the actuation trigger 280. Actuationof trigger 280 will move tube 220 proximally and distally with respectto tube 240. Actuating the trigger 280 will allow the stent 10 to bereleased from the tubes 220 and 240.

[0042] The stent and distal end of the instrument 200 are inserted intothe urethra 410 through the meatus 400 of the patient's penis as seen inFIGS. 8 and 9. The distal end of the instrument 200 and the stent 10 aremanipulated through the urethra 410 such that the prostatic section ofthe stent is located within the prostatic urethra 411 and the distal endof the stent is distal to the external sphincter 430, thereby providingan open passage for urine from bladder 450 through the lumen of theurethra. Then, the application instrument 200 is withdrawn from theurethra 410 by engaging trigger 280 and pulling distally on theinstrument, thereby completing the procedure and providing for animplanted stent 10 which allows for patency of the urethral lumen 410.As seen in FIG. 9, the stent 10 after having been in place for theappropriate period of time has been converted into a state wherein it issubstantially a soft, flexible filament, and is readily passed from theurethra 410 out of the patient's body with the urine flow, or ismanually pulled out of the lumen. It will be appreciated by thoseskilled in the art that placement for other types of body lumens couldbe done in a similar manner, with modification as required by the uniquecharacteristics of the lumen or of the surgical emplacement procedure.

[0043] The following examples are illustrative of the principles andpractice of the present invention, although not limited thereto.

EXAMPLE 1

[0044] Manufacture of Removable Fiber by Extrusion Coating Process.

[0045] A polydiaxanone (PDS) homopolymer was added to a nitrogen purgedhopper of a ¾″ vertical single screw extruder with a 24:1(Length:Diameter) standard screw. The temperature profile of theextruder was 250, 260, 270 and 275 degrees (F) from rear zone to die.The screw speed was 6.5 RPM and the adapt pressure was 1345 psi. A B&H30 cross head (B&H Tool, Inc., San Marcos, Calif.) was employed with a0.020-inch diameter guide (pressure tip) and a 0.048-inch diameter die.An 0.018-inch diameter non-degradabe polyester braided filament (soldunder the tradename ETHIBOND, by Ethicon, Inc., Somerville, N.J.) wasguided through the cross head. The fiber was coated with moltenpolydioxanone, chilled in a water trough, dried by a air wiper, takenoff and sequentially spooled. The temperature of the water trough was 8°C. The take-off speed was 2.1 meter/min. The fiber, with the outerdiameter of 0.044-inch, was stored in a nitrogen environment.

EXAMPLE 2

[0046] Manufacture of Stent Using the Coated Filament

[0047] A string was tied so that it created a small loop through thefirst hole C of the mandrel (see FIG. 10). Two metal posts (mm diameter2×15 mm length) were inserted into the holes A and B.

[0048] Posts were placed in holes A and B. The C-side end of the mandrelwas clamped inside the collet of a winding motor. A 5-foot long coatedfilament was passed through the loop. The fiber was folded. The two freeends were held together and the folded fiber was stretched loosely sothat the loop was positioned to be in the approximate center of thefiber. The folded filaments were loosely held together to make sure thatthe coils were packed adjacent to each other. The winding speed wasbetween 20-30 RPM for the length of the Prostatic Section.

[0049] Once the first post (B) was reached, the fiber was then bent overthe post toward the distal section. Winding an additional 180° moreformed the connector between posts (A) and (B). The filament was thenpositioned tangent to the mandrel and the distal loop was then coiled ina similar fashion as the Prostatic Section. An adjustable clamp was usedto secure the filament to the mandrel. The assembly was stored undervacuum for 48 hours to allow it to dry prior to annealing.

[0050] Prior to annealing, the posts (A) and (B) were removed from themandrel. The entire assembly was suspended in an annealing oven andheated at 80° C. for 10 hours in a vacuum environment. The stent wasremoved from the mandrel, trimmed, and stored in nitrogen environment.

EXAMPLE 3

[0051] A male patient is appropriately anesthetized and undergoes aprostrate thermal ablation procedure using conventional laser treatmentdevices. After successful completion of the surgical procedure, a stent10 of the present invention is inserted into the patient's urethra andbladder in the following manner using an applicator 200. The surgeontrims the Prostatic Section of the stent to size. The stent is placed atthe end of the applicator. A conventional cystoscopic telescope isinserted into the lumen of the applicator. The stent and applicator arelubricated with a water soluble medical grade lubricant. A fluidreservoir is attached to the applier as in any standard cystoscopyprocedure. The stent is placed in the prostatic urethra under directvisualization using the applicator. Once positioned correctly, theapplicator is removed, leaving behind the stent in the prostaticurethra. In approximately 28 days after implantation, the outer coatingdegrades, thereby converting the stent into a soft, flexible filamentarystructure that is removed from the urinary tract by grasping the end ofthe filament and pulling it from the lumen.

[0052] The stents of the present invention provide many advantages overthe stents of the prior art. The advantages include: rigidity (lumenpatency) for a prescribed time; a degradation/absorption softeningmechanism, whereby the stent softens into a readily passable/removablefilament; biocompatibility; means to prevent migration; means tonon-invasively monitor the stent and its position by X-ray, etc.

[0053] Although this invention has been shown and described with respectto detailed embodiments thereof, it will be understood by those skilledin the art that various changes in form and detail may be made withoutdeparting from the spirit and scope of the claimed invention.

We claim:
 1. A stent, comprising: a helical structure having a pluralityof coils, said structure having a longitudinal axis and said coilshaving a pitch, said structure having an internal longitudinal passagewherein said structure is made from a filament having a cross-sectionand an outer surface, said filament comprising: a soft flexibleelongated member having an outer surface; and a bioabsorbable orbiodegradable polymeric outer coating on the outer surface of themember; wherein, the polymeric coating has sufficient mechanicalintegrity to effectively maintain the flexible member in a helicalconfiguration, until the coating has sufficiently been degraded orabsorbed in vivo to effectively convert the helical structure back intoa soft, elongated member.
 2. The stent of claim 1, wherein the coatingcomprises a melt polymer.
 3. The stent of claim 1, wherein the coatingcomprises a solution polymer.
 4. The stent of claim 1 wherein thefilament comprises a surgical suture.
 5. The stent of claim 4, whereinthe suture comprises a monofilament.
 6. The stent of claim 4, whereinthe suture comprises a multifilament.
 7. The stent of claim 4, whereinthe suture comprises a non-absorbable suture.
 8. The stent of claim 4wherein the suture comprises an absorbable suture.
 9. The stent of claim1, wherein the coating comprises a polymer made from monomers selectedfrom the group consisting of lactide, glycolide, para-dioxanone,caprolactone, and trimethylene carbonate, blends thereof and copolymersthereof.
 10. The stent of claim 1, wherein the polymer of the coatinghas a glass transition temperature above 55° C.
 11. The stent of claim 1wherein the polymer of the coating has a glass transition temperatureabove 120° C.
 12. The stent of claim 1, wherein the polymeric coatingcomprise a polymer selected from the group consisting ofpolyacrylamides, polyethylene glycols, polyethylene oxide, vinylalcohols, and poly(N-vinyl pyrrolidone)s.
 13. The stent of claim 1,wherein the polymeric coating additionally comprises polyamide.
 14. Abiodegradable filament, the filament comprising: an elongated, flexiblemember having a cross-section, and an outer surface; and, a polymericcoating on said outer surface, said coating comprising a biodegradableor bioabsorbable polymer, wherein, the polymeric coating has sufficientmechanical integrity to effectively maintain the flexible member in asubstantially fixed configuration, until the coating has sufficientlybeen degraded or absorbed in vivo to effectively convert the structureback into a soft, elongated member.
 15. The filament of claim 14,wherein the coating comprises a melt polymer.
 16. The filament of claim14, wherein the coating comprises a solution polymer.
 17. The filamentof claim 14, wherein the filament comprises a surgical suture.
 18. Thefilament of claim 17, wherein the suture comprises a monofilament. 19.The filament of claim 17, wherein the suture comprises a multifilament.20. The filament of claim 17, wherein the suture comprises anon-absorbable suture.
 21. The filament of claim 17 wherein the suturecomprises an absorbable suture.
 22. The filament of claim 14, whereinthe coating comprises a polymer made from monomers selected from thegroup consisting of lactide, glycolide, para-dioxanone, caprolactone,and trimethylene carbonate, blends thereof and copolymers thereof. 23.The filament of claim 14, wherein the polymer of the coating has a glasstransition temperature above 55° C.
 24. The filament of claim 14 whereinthe polymer of the coating has a glass transition temperature above 120°C.
 25. The filament of claim 14, wherein the polymeric coating comprisea polymer selected from the group consisting of polyacrylamides,polyethylene glycols, polyethylene oxide, vinyl alochols, andpoly(N-vinyl pyrrolidone)s.
 26. The filament of claim 14, wherein thepolymeric coating additionally comprises polyamide.
 27. A method ofmaintaining a passageway of a body lumen substantially open, comprisingthe steps of: providing a stent, said stent comprising: a helicalstructure having a plurality of coils, said structure having alongitudinal axis and a longitudinal passage, and said coils having apitch, wherein said structure is made from a fiber, said fiber having across-section and said filament comprising: an elongated flexible,filament member, having an external surface and a cross-section; and, apolymeric outer coating on the surface of the member, wherein, thepolymeric coating has sufficient mechanical integrity to effectivelymaintain the flexible member in a helical configuration; and, implantingsaid stent in a body lumen and maintaining the stent in the body lumenfor a sufficient period of time to effectively maintain the passagewayof the lumen substantially open for a desired period of time until theexterior coating softens, thereby converting the stent structure into asoft, flexible filamentary structure.